Method of forming resistor units



' July Z6, 1931. L. E. POWER METHOD OF FORMING RESISTOR UNI-TS Filed June 10, 1927 Patented July 28,. 1931 UNITED STATES PATENT OFFICE LAURENCE E, POWER, OF MILWAUKEE, WISCONSIN, .ASSIGNOR, BY MESNE ASSIQ N- MENTS, OF ONE-HALF TO LYNDE BRADLEY 1ND ONE-HALF TO HARRY I. BRADLEY,

BOTH OF MILWAUKEE, WISCONSIN METHOD OF FORMING RESISTOR UNITS Application filed June 10,

This invention contemplates as an object the provision of an improved resistor unit which will be of extremely neat design, reliable in operation and capable of production at a very low cost.

It is another object of this invention to provide an improved resistor unit having its ends of lower resistance value than its medial portion to provide a good electrical connection with mounting clips and thus eliminate the end, metallic terminal members.

And a still further object of this invention resides in the provision of an improved resistor unit and method of forming the same whereby the unit is rendered moistureproof to insure its constancy in atmospheres of various temperature and various degrees of humidity.

VViththe above and other objects in view WhlCl'l will appear as the description pro ceeds, my invention resides in the novel construction, combinatlon and arrangement OI parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindiselosed invention may be made as come Within the -"scope of the claims.

In the accompanying drawings, I have illustrated one complete example of the physical embodiment of my invention cons tructed according to the best mode I have so far devised for the practicalapplication of the principles thereof, and in which:

Figure l is a side elevational view of my improved resistor unit mounted between a pair of spring terminal clips;

Figure 2 is an enlarged view thereof, partly in side elevation, with one end portion broken away and in section, and

Figure 3' is a side elevational view of an improved resistor unit built in accordance with my improved methdd and having a moisture-proof covering, one end portion of which is broken away.

Referring now H1016 particularly to the accompanying drawings, 5 designates a resistor unit which is preferably of rod shape having its'endsfi tapered to fit within the 1927. Serial No. 197,881.

thoroughly mixed and formed under high pressure in the presence of heat apredetermined resistance value being obtained by controlling the proportions of the mixture alone or by the controlling the mixture and subjecting it to. an electrical current in the manner described at length in the co-pending application of Lynde Bradley, filed August 31, 1925, Serial No. 53,570.

The ingredients entering into the intermediate portion of the unit, as defined by the points a-b, consist of approximately four and one-half per cent conducting material, such' as graphite and the like, while the ingredients entering into the end portions 9 of the unit consist of approximately thirteen and one-half per cent conducting material, although it is expressly understood that these portions may be varied depending upon the resistance Value it is desired to produce in the unit. The three batches of ingredients, two of which are identical, are placed in the same mold, the batch for one end being first placed therein,

the batch for the intermediate portion next and the batch for theother end last, are subjected to molding pressure producing the,

for, when a resistor unit not equipped with metal end terminals is placed between the clips, the resistance between the unit and the clips frequently ishigher than the resistance of the unit itself due to the fact that the resistance material rather than conductive. material of the unit is in contact with the metal of the clips. Consequently, with the unit in one position, the resistance in the circuit is of one value and turning of the unit frequently causes a material change in the circuit resistance.

However, with the unit having its ends formed of ingredients having a greater portion of conductive materials, it has been demonstrated that the contact between the unit and the clips is good at all times and turning of the unit in no wise changes the circuit resistance. This type of unitalso permits an economy in manufacture in that instead or" necessitating the capping oi": the ends of the unit by metallic terminals, such as in the application aforementioned, it is a merely necessary that slugs of the diiierent v types be dropped in the forming mold.

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After the unit is formed, it may be protected against the efiects of moisture by 4 being placed in melted paraflin or other like.

material within an evacuated vessel, as a result of which the pores of the unit are emptied of air and moisture. The -vacuum is then relieved, the parafiin or other material entering the pores completely filling the same so that a thin film completely covers the unit, the ends of the unit being wiped or burnished so that their electrical contact with the terminal 7 is assured.

If desired, a tube or wrapping of paper or other material 10 may be secured over the unit prior to its paraflin bath, in the manner above described, to give added protection, the wrapping having a suitable designation 11 thereon to indicate the resistance value of the unit.

What ll claim as my invention is 1. The hereindescribed method of forming a molded resistance unit having terminal portions of relatively high conductivity, which consists in providing a material of relatively high resistance value, in placing a material of lower resistance value at the ends of the material of higher resistance value, and in molding the material in a single operation into an integral unit.

2. The hereindescribed method of forming a molded integral resistance unit having terminal portions, which consists in providing two materials of different resistance values, in dividing the material of least resistance and disposing the-other material thcrebetween, and in a single operation molding the materials into an "integral unit with its terminal portions formed of the material of least resistance, the juncture between the two materials being substantially abrupt. I 3. The hereindescribed method of forming a molded resistance unit having terminal signature.

LAURENCE 1E. POWER. 

